1. Field of the Invention
This invention relates to a laser induced liquid jet generating apparatus which serves the purpose of irradiating a laser beam against a liquid thereby generating a liquid jet flow and utilizing the jet flow to shatter a target object such as thrombus, and recovering the shattered object.
2. Description of the Related Art
In recent years, as a means to cure the thrombosis which obstructs the human blood vessel, the method which consists in generating a liquid jet flow with a laser beam and physically breaking the clot with the jet flow is prevailing. This method has been awakening a great expectation for the therapy of the thrombosis because it promises early resumption of the blood flow without requiring administration of a large amount of a thrombus-dissolving agent which brings a serious secondary effect. Particularly, when the cerebral tissue remains in the state of ischemia for not less than six hours, it is held that the restoration from the neuropathic symptom is difficult to attain. When the blood flow recurs in a few hours after the crisis, the method brings a very high curative effect.
The official gazette of JP-A-2003-111766, WO00/04838 (the official gazette of International Unexamined Patent Publication No. 2002-521084), and THE JOURNAL OF JAPAN SOCIETY FOR LASER SURGERY AND MEDICINE, Vol. 22, No. 3 (2001) (refer to page 217) describe a technique which comprises guiding a laser in a pulsating form from a laser oscillator into an optical fiber inserted in a catheter, abruptly heating a physiological saline filling the catheter interior and inducing a liquid jet flow, and shattering and removing the thrombosis by dint of the liquid jet flow.
Since this method guides the catheter having the optical fiber inserted therein close to the thrombosis, for example, and generates the liquid jet flow and, therefore, enables the power of the liquid jet flow to reach the thrombosis without any decline of the power, it is capable of acquiring a high therapeutic effect.
The catheter to be inserted into the blood vessel is very slender. Further, when it is used in the state of having an optical fiber inserted therein, it keeps the optical fiber itself from increasing its thickness, imposes a limit on the intensity of the laser beam, and renders irradiation of a powerful laser beam difficult. The method, therefore, is possibly incapable of generating a powerful liquid jet flow and effecting necessary shattering of the target object such as the thrombosis, for example, sufficiently.
The conventional catheter is a long slender tube formed of vinyl chloride or PCB (poly-chlorobiphenyl) or, as disclosed in WO00-04838 (the official gazette of International Unexamined Patent Publication No. 2002-521084), of such a material as polypropylene or polyimide. Since it is soft throughout the entire volume so as to be deformed along the meandering blood vessel, it tends to be thermally affected when it is exposed to a powerful laser beam.
Particularly, when the optical fiber having an outside diameter (core diameter) of about 0.4 mm is inserted into a catheter of a small diameter (generally about 0.9 mm), only an extremely small gap is allowed to exist between the inner surface of the catheter and the outer surface of the optical fiber. When they are exposed to a powerful laser beam, the heat of the laser beam is conducted to the catheter and the catheter is consequently fused and deformed and made to obstruct smooth discharge of a liquid jet flow and curtail its own service life.
Further, since the catheter of this nature is only capable of shattering the target object such as the thrombus but is devoid of a means to recover the shattered target object, the thrombus which has been shattered is suffered to float in the blood vessel. When the floating fragments of the thrombus happen to get caught in the blood vessel, they will possible form a main cause for the generation of a new thrombus. It is conceivable to provide the catheter used exclusively for shattering the thrombus with a separate tube used exclusively for absorbing the thrombus. When these catheter and tube are inserted into the blood vessel, they bring the disadvantage of aggravating the burden imposed on the human body.